Photoelectric exposure meter



Fgb. 14, 1939. A BERNHARD ET AL ,1 5

PHOTOELEGTR IC EXPOSURE METER Original Filed March 14, 1935 PatentedFeb. 14, 1939 UNlTED STATES PATENT OFFICE PHOTOELEOTRIC EXPOSURE METERcompany of Germany Original application March 14, 1935, Serial No.11,140. Divided and this application July 13, 1937, Serial No. 153,416.In Germany March 4 Claims.

This application is a division of our original Patent application No.11,140 filed on March 14, 1935, on which Patent No. 2,092,826 has beenissued.

The present invention relates to a photoelectric exposure meter of thetype comprising a photo-electric element and a direct current measuringinstrument. Apparatus of this kind usually comprise an adjustable irisdiaphragm arranged in front of the photo-electric element which enablesthe stop adjustment and plate sensitivity to be used for the particularexposure to be taken into account in the measurement.

It is an object of the present invention to provide an exposure meterwherein an adjustable iris diaphragm is dispensed with.

A further object of the invention is to provide a photoelectric exposuremeter comprising a plurality of scales inter-related in such a mannerthat exposure times may be derived from the photo-electric indication,for different stops and plate sensitivities.

A still further object of the invention is to provide an exposure meterin which a photo-electrio-indication may be interpolated for a selectedplate sensitivity and stop value to establish the corresponding exposuretime.

Still another object of the invention is to provide a photo-electricexposure meter wherein manually operable means are provided which can beset in accordance with a given plate sensi= tivity and/or stop valueto-interpolate a photoelectric indication into a corresponding exposuretime for the given plate sensitivity and a stop value.

Further objects of the invention will be ap parent from the descriptionas it proceeds.

In order that the invention may be more clearly understood someembodiments thereof are dcscribed hereinafter with reference to theaccompanying drawings in which:

Fig. 1 is a cross-sectional view of one form of exposure meter accordingto the invention;

Fig. 2 is a front view of the meter shown in Fig. 1;.

Fig. 3 is a front view of a further embodiment of the invention;

Fig. 4 is a modification of the device shown in Fig. 3.

In Figs. 1 and 2 an exposure meter is shown comprising a casing I, aphoto-electric element 2, and a protective disc 3. The current measuringinstrument comprises the magnet I, the scale 5 and the pointer 6, whichis visible through an aperture I in the casing. The measuring scale 5 isdivided into non-uniform (logarithmic) divisions m representing exposuretimes, corresponding to a given stop and agiven plate sensitivity, thescale divisions m being somewhat more widely spaced at the centre owingto the 5 non-uniform distribution of the field between the poles of thepermanent magnet. In order to facilitate the interpolation of theexposure times read off, for different stops and/0r plate sensitivities,a member 8 is rotatably mounted on the casing of the exposure meter. Themember 8 carries at one end a scale calibrated in the usual stop valuesI, which moves over a scale s divided in the usual exposure times. Atthe other end, the slide carries a scale divided in plate sensi--tivities (26, 23, 19 Sch.) which moves over a uniform scale a. providedon the scale 5 and the divisions of which are linked up with themeasuring scale m by means of oblique connecting strokes 1. As canreadily be seen, it is possible to bring the scale of stops f into thecorrect position relative to the lower scale s of exposure times, byrotating the member 8 for each exposure time value read off, into theappropriate position for the individual reading, in accordance with theappropriate one of the given plate sensitivities (or some intermediatevalue), so that for each stop the corresponding exposure time can beread off.

The uniform auxiliary scale a, and possibly the measuring scale m alsomay be arranged outside, on the trout cover of the casing. The pointer6, as illustrated in Fig. 4, being visible through an opening 9 in thecasing cover. Preferably, however, the measuring scale m and theauxiliary scale a are arranged on an inner scale dial 5, which isarranged in front of the pointer 6 and has an opening it through whichthe pointer 8 can be viewed, as shown in Fig. 3, The measuring scale mis preferably calibrated for the stop N63 and 26 Sch. so that for thesevalues the question of interpolation of the results does not arise.However, as is illustrated in Fig. 4, the measuring scale m may also beleft unmarked, so that the member 8 must be adjusted after eachmeasurement. The angle at subtended by the auxiliary scale a is'made aslarge as possible, preferably as much as possible greater than 90, sothat the connecting lines I for the auxiliary scale a are short andstraight and so that a great arc length is obtained for the lower timescale s and also for the movement of the rotary member 8. Y

The arrangement may be so devised that the centre ll of the rotarymember 8 coincides with uniform auxiliary scale a clearlydistinguishable,

they may advantageously be executed in alternateiy difierent colours ordistinguished in some other way.

We claim;-

1. Exposure meter comprising a casing having a substantially fiat frontwall, a photo-electric element and a direct current measuring instrumentboth mounted within said casing and electrically connected together,said measuring instrument including a rotatable shaft operated therebyand arranged at right angles to said front wall, a pointer on said shaftadapted to move in an arcuate path behind said front wall and in a planeparallel thereto, a measuring scale fixed adjacent said pointer forindicating deflections thereof, a window in the upper part of said frontwall and in' front of said pointer, an arcuate fixed scale on the lowerpart ofsaid front wall, a flat, at least partially, sector shaped memberrotatably pivoted in the middle part of said front wall, and two scaleson said member and rotatable therewith, one of which being adjacent toand cooperating with said measuring scale and the other adjacent to andcooperating with said fixed scale, said fixed and rotatable scalesindicating exposure times, plate sensitivities and stop values.

\ 2. Exposure meter asdefined in claiml, wherein the said sector shapedmember is pivoted between the centre of said casing and the shaft ofsaid measuring instrument.

3. Exposure meter comprising a casing having a substantially fiat frontwall, a photo-electric element and a direct current measuringinstruarealsae therewith, one of said rotatable scales being adjacent toand cooperating with said uniform measuring scale and the other of saidtwo rotat-,

able scales being adjacent to and cooperating with said fixed scale,said fixed and said two rotatable scales indicating exposure times,plate 'sensitivitiesand stop values.

4. Exposure meter comprising a casing having a substantially fiat frontwall, a photo-electric" element and a direct current measuringinstrument both mounted within said casing and electrically connectedtogether, a pointer operated by said measuring instrument and adapted tomove in an arcuate path behind said front wall, an arcuate non-uniformmeasuring scale fixed adjacent said pointer such that said pointerindicates values on said non-uniform scale, an armate uniform measuringscale fixed adjacent said non-uniform scale and division-by-divisiontherewith, a fixed scale of exposure times on said front wall, a fiatmember rotatabiy pivoted in said front well, a scale of platesensitivities and a scale of stop values both on said member androtatable therewith, the said scale of plate sensitivities beingadjacent to and cooperating with said uniformv measuring scale, and saidscale of stop values being adjacent to and cooperating with said scaleof exposure times.

ALBRECHT BERNHARD.

GUJDO BEYRICH.

HANS HABERMANN.

